Unlicensed spectrum is available for usage by any technology such as Bluetooth, Wi-Fi, or the like, unlike the licensed band operation where explicit licenses must be obtained for supporting transmissions. The current unlicensed bands include 2.4 GHz, 3.5 GHz, 5 GHz, and 60 GHz. The existing methods propose deployment of long term evolution (LTE) in the unlicensed 5 GHz spectrum while addressing the co-existence with Wi-Fi nodes. There are requirements for considering the co-existence of 5th generation (5G) technology in the unlicensed bands. The next generation radio access technologies (RAT) has to support efficient mechanisms for sharing the unlicensed spectrum with other international mobile telecommunications (IMT)/non-IMT systems. As such, it is necessary to mitigate issues which can hamper the co-existence of LTE with Wi-Fi.
LTE-unlicensed (LTE-U) is the technology, where LTE co-exists with Wi-Fi nodes in the 5 GHz unlicensed spectrum. The standards for the LTE-U in a downlink have been finalized in the Release-13. In Release-14, work related to uplink transmission in the LTE-U spectrum initiated. The LTE-U is having two variants, viz., LTE-U and licensed assisted access (LAA). The LTE-U relies on a carrier sense adaptive transmission, in which there is a discontinuous transmission for coexistence with the Wi-Fi nodes. In the LAA, a dedicated primary cell (P-Cell) exists in a licensed band that can coordinate some of the actions in the unlicensed spectrum.
5G is touted as the next big-thing in wireless industry. 3rd generation partnership project (3GPP) has started specification studies for 5G systems. One of the two key distinctions to be considered for the study of 5G systems is frequency of operation. Specifically, studies consider either the portion of the unlicensed spectrum which is less than 6 GHz or the portion of the unlicensed spectrum which is greater than 6 GHz. For 5G systems operating in the portion of the unlicensed spectrum, less than 6 GHz, and co-existing with other nodes (Wi-Fi) in the unlicensed spectrum, follow the design principles of the LAA and enhanced LAA (eLAA) technologies. However, this is not the case for 5G systems which operate in the portion of the unlicensed spectrum which is greater than 6 GHz. In this spectrum beamforming is the primary technology enabler. Hence, appropriate techniques that suit this primary technology enabler have to be investigated.
Energy detection is proposed as the enabling mechanism to be utilized for channel sensing in LTE-U technology. Since energy detection is the most widely used method for spectrum sensing, it can be used in 5G systems in the unlicensed bands. When, a node, i.e., either a user equipment (UE) or evolved node B (eNB), senses the channel for some period of time (sensing mechanism is completely defined by the listen before talk (LBT) procedures) and if the energy levels are below a predefined threshold, then the node declares that the channel is free and thereafter proceeds with its transmissions. While the LBT procedures are defined with respect to the LTE technology, similar procedures will be developed for 5G systems as part of the 5G specifications.
The simple sensing techniques such as energy detection are prone to errors due to adjacent channel leakage. In an example, if a first UE (UE 1) is occupying channel 1 and a second UE (UE 2) is occupying channel 2. Prior to performing uplink transmission, the UE 2 intends to sense whether or not the channel 2 (which is adjacent to channel 1) is free. In order to perform the sensing procedure, the UE 2 performs energy detection. The UE 2 may, or may not, determine that the channel 2 is free. The cause of not being able to determine that the channel 2 is free, is primarily due to the leakage (spectral emission) across channel 1 and channel 2, due to interference from the transmissions of UE 1. It can be depicted through experimental studies that the leakage can be as high as 15 dB, which can prevent (depending on the power levels at which UE 1 is transmitting on channel 1) channel 2 to be used by the UE 2 for performing uplink transmissions, although there are no Wi-Fi nodes operating in the spectrum of the channel 2.
Therefore it is necessary to address the issue of spectral emission when the eNB intends to schedule multiple UE's across various channels in the unlicensed spectrum. Furthermore, the different unlicensed carriers to be used by the eNB for scheduling uplink transmissions by multiple UEs are synchronized in time. Spectral emission also leads to complications in scheduling multiple UEs in adjacent frequency bands of the unlicensed spectrum.
In 5G systems, with beamforming capabilities (specifically in the 6 GHz spectrum), multiple UEs are scheduled across beams. There are circumstances, wherein the different beams allocated to different UEs are not sufficiently separated spatially. Spectral emission occurs across beams either due to overlap of the different beams and side lobes, and various other spectral emission mechanisms.
Thus, there is a need of having a method which allows efficient radio resource utilization by a single or a plurality of UEs in the LTE-U systems.
There is also a need of having a method for enhancing the performance of the LTE systems and 5G systems in LTE-U systems.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.